Volume control



Nov. 1, 1932;

s. TAR ZIAN VOLUME CONTROL Filed July 8. 1930 3 Sheets-Sheet 1 PLA TE VOLT/1 5E.

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VOLUME CONTROL Filed July 8, 1930 a Sheets-Sheet 2 INVE TOR. I M La M BY [WM/M1 :(Qzii 13 ATTORNEY Nov. 1, 1932., s. TARZIAN 1,335,307 I VOLUME CONTROL Filed July 8. 1930 3 Sheets-Sheet 3 BY -x 1211 ATTORNEY Patented Nov. 1, 1932 UNITED T TES .PATEN'II- OFFICE.

sanxEs'rAnziAN, or PHILADELPHIA, rENNsYLvANIAflnssIoN oa 'ro a'rwa'rnn KENT MANUFACTURING COMPANY, or PHILADELPHIA, PENNSYLVANIA, A conPonA'rIoN or rnNNsYLvANIA vournn coN'rno Application filed Jul 9,1930. Serial No. 466,372.

My invention relates to radio receiving apnitude of amplification of a screen grid tuber amplifier is varied while maintaining the internal late impedance or resistance of the tube su stantially constant or permitting it v to vary within suitable limits, by simultaneously controlling or varying, preferably by uni-control, the plate voltage and either the magnitude of negative bias upon the control grid, or, and preferably, the magnitudeof 30 the screen grid voltage. p I I Further m accordance with my invention, the magnitude of the signal input voltage impressed upon one of the tubes of ,the re- .ceiving'system, particularly a tube controlled as aforesaid, is varied or controlled in combination or association with the aforesaid dual control, particularly to maintain high quality of reproduction, which otherwise would or might be seriously affected, particularly in the case of extreme reduction or amplification occasioned by stron signals.

Further in accor ance with my invention, the control of plate voltage andof negative bias of the control grid or of screen grid volt- 5 a e may be efiecte upon each of a plurality 0% cascaded amplifier tubes; and further in accordance with my invention, at or in ad-. vance of the input of the first stage of tubes so cascaded and controlled there may be simultaneously effected the aforesaid control of input signal voltage.

Further in accordance with my invention, durin the control of screen grid voltage in anyo the relations aforesaid, the ratio of the screen grid voltage tothe plate voltage may be varied or, and preferably, maintained'at a suitable and definite ma itude.

My invention resides 1n a system of controls of the character hereinafter described and claimed.

For an understanding of my invention and for an-illustration of some of the forms it may take, reference is to be had to the accompanying drawings, in which Figs. 1, 2 and 3 comprise, respectively, curves or graphs illustrating the characteristics of screen grid tubes. I

Fig. 4 is a diagrammatic view of a superheterodyne receiving circuit involving controls of plate and screen grid voltages, and of input signal voltage.

Fig. 5 is a diagrammatic view of a superheterodyne receiving system involving controls of late voltage, negative bias upon con- 'trol gri and input signal voltage.

Referring to Fig. 1, there are shown characteristic curves of screen. grid tubes in general, and particularly of the present UV 224 Radiotron type, normally operating with a negative bias of 1.5 volts on the control grid volts positive bias on the screen grid, an

2.5 volts upon the cathode heater. Abscissw are plate voltages for all three curves, while ordinates are conductance's, in micromhos, for the mutual conductance curve Gm, mag-- nitudes of the factor of amplification for the curve Mu, and resistance, in megohms,-for the curve the tube.

- From Fig. 1 it will be noted that as late voltage decreases the plate resistance Yp of internal plate resistances of thev gecreases, as does also the amplification factor Mu, while the mutual conductance Gm remains substantially constant, which is in effect substantially constant amplification by the tube when having an external plate load or im edance, as is necessary in practice.

In ig. 2, for atube similar to that to which Fig. 1 relates, abscissae are screen grid voltages, while for the mutual conductance characteristic Gm the ordinates are mutual conductances in micromhos; for the curve Mu the ordinates are magnitudes of amplification factor; and for the curve Yp, internal plate resistance, the ordinates are resistances 1n megohms. 'With the plate voltage maintained constant, say at a normal voltage of 180 volts, with decrease of screen grid voltage or ositive bias, the'mutual conductance or amp ification decreases, while at the same time the internal plate resistance of the tube increases.

In accordance with my inventionby simultaneously and at suitably relative rates 5 decreasing the plate voltage and the screen ,grid voltage, the mutual conductance or amplification may be very greatly reduced, for

purposes of volume control or otherwise, while the internal plate resistance of the w tube remains substantially constant or varies only between rather narrow limits, and in any case may be kept comparable to or within a relatively low ratio of magnitude with respect to the external plate impedance.

By the simultaneous control of the plate and screen grid voltages and in the same sense, the effect of decreasing internal plate resistance by decrease of plate voltage, Fig. 1, is offset or compensated for more or less completely or accurately by the increase in internal plate impedance, due to decrease in screen grid voltage, Fig. 2. In consequence, amplification may to great extent be varied with unimportant or small change in plate impedance. v

In lieu of varying screen grid voltage for the purposes aforesaid the magnitude of negative bias upon the control grid may be varied along with variation of plate voltage with substantially like effect. This is illustrated by the characteristic curves in Fig. 3, where a tube of the same average characteristics contemplated by Figs. 1 and 2 has a plate voltage of 180 volts, 75 volts on the screen grid and 2.5 volts on the cathode heater. In this figure, abscissae are negative bias voltages uponthe control grid, the ordinates for the mutual conductance curve Gm are again mutual conductances in mi- 40 cromhos, and for the amplification factor curve Mu the ordinates are magnitudes of that factor, and for the internal plate resistance curve Yp the ordinates are resistances in megohms. As indicated, by decreasing the absolute voltage of the control grid, i. e., increasing the magnitude of negative bias thereon, the internal plate impedance rises, while the mutual conductance or amplification decreases. The curvesYp and Gm of Figs. 2 and 3 accord, in kind or sense of variation, with those in Figs. 2 and 3. In general, the effect of increasing negative bias upon the control grid has the same effect upon increase in'internal plate resistance and mutual conductance or amplification that obtains in event of decrease of screen grid voltage. Comparing Figs. 1 and 3, therefore, the effect of decrease of plate voltage upon internal plate resistance is offset by increasing the magnitude of negative bias upon control grid, so that while decreasing amplification, eurve Gm of Fig. 3, the internal plate resistance is maintained constant or varies inconsequentially or unimportantly, and maintains roughly a given neeaaov Referring to Fig. 4, which illustrates the significant portion of a superheterodyne system, D is the first detector upon whose input electrodes, control rid and cathode, is impressed the radio requency voltage representing the signal or message, including speech and music. In advance of this tube may be any suitable timing or selective system for tuning to the frequency of the desired signal while discriminating against all other frequencies, including those which producev the same beat frequency by reaction with the locally generated oscillations. The generator of local oscillations is diagrammatically indicated at O, impressing the oscillations generated upon the input system of the detector D through the transformer t. The. frequency of the oscillations produced by the generator 0 are varied to produce at all frequencies of desired signals the same heat or intermediate frequency. i

. The voltage of intermediate,frequency, for example of the order ni-""130 kilocycles for present broadcast reception, appearing int-he plate circuitof the detector D, is impressed upon the input system of the first screen grid intermediate frequency amplifier tube V, which amplifies the current of intermediate frequency. Its plate circuit is coupled to the input of a second like intermediate frequency, amplifier tube V1 in whose plate circuit appears a current of intermediate frequency of still greater magnitude. That plate circuit is suitablycoupled to the input of the second detector tube V2, which is coupled to a suitable audio frequency amplifier tube, or several of them 1n cascade,

with the last of which, 'which may be a pushpull combination, may be associated a signal translating instrument, commonly a loud speaker.

In the vacuum tubes referred to, the control grids are indicated at 9, screen or shield 'grids at 8, the cathodes at c, (in these cases heated by the heaters h), and anodes or plates at The source of power may be anything suitable or convenient, as direct current from a power lme or battery, or, as illustrated,

from an alternating current lighting or power system whose line conductors are indicated at 1 and 2. Across these conductors is the primary of a transformer T, having a secondary S1 associated with the double wave rectifier tube V3, having a filament or cathode f heated by current from the secondary S2 for supplying the high voltage or" plate circuit current in the form of rectified and filtered current, the filter system comprising usual inductances and ca acities, as indicated. Secondar S3 supp ies current to the cathode'heaters or directly to filaments if used as cathodes. The terminals of the high potential source for the plate circuits of thetubes of the receiving system are indicated at S and 4, the latter generally at ground potential or at potential of the base or chassis of the receivi1 1g set, and 3 being the terminal betweenwhich and terminal 4 exists a difference of potential of saydfiO volts. The direct current field windingof the signal translating instrument 'or electrodynamic loud speaker is indicated at F.

V V1,-are supplied throughchokecoils b or The plate c rcuits of the tubes D, V, and

an other suitable arrangements %or the tubes V, V1, there'is prov ded a potentiometer resistance P, of say 110,000

ohmsconnected between thev high potential terminal 3 and the terminal 4 or, what is the same thing, the ground or chassis terminal E. Thecommon lead\5 for the late circuit supplies of the' tubes V and V1, is connected to the contact 6 movable along the potentiometer resistance P, whereby the voltage impressed upon the plates a of the tubes"V and V1 may be varied for the purposes herein described. The conductor 7 serves in common to the screen grids s of the tubes V and V1 for impressing thereon a suitable positive bias voltage, which is variablenvith variation of the-plate voltage for these tubes andin the same direction or sense. This .is accomplished, by connecting the conductor 7 to a point 8 of the resistance comprising the portions R and R1, connected in series between the aforesaid slider contact 6 and terminal 4, or ground E. As indicated, the

connection at point 8 is permanent, resulting in a substantially fixed ratio between the screen gridand plate voltages of and for the tubes V and V1, Whatever may be the plate voltage magnitude. For example, the sections R and R1 may have resistances of about 20,000 and 60,000 ohms respectively, whereby, throughout the variation of plate voltage for the tubes V and V1, the screengrid voltage will be about one-half thereof.

It shall be understood that in any event by thesecor equivalent means, the screen voltage is, throughout the variation of the platevoltage, of such relative magnitude as to maintain the internal late resistance substantially constant or wit in suitably narrow limits.

It will be understood, however, that at the end 8 of the conductor 7 may be a slider contactmovable along the resistance R, R1, to effect suitable variation of ratio of screen grid to plate voltages as they are varied to-,

05 gether in the same direction or sense. Such slider contact may be actuated through suitable mechanical connection in unison with contact 6 and any other contacts actuated in unisonwith the latter. Ordina'ril and preferably, a fixed connection 8 is utilized.

In the arrangement shown, theplate and screen grid voltages of the tubes in question are simultaneously varied byniovement of the single contact, 6. However, the screen grid voltage may be obtained by contact, at

.end 8 of conductor 7,'movable along the resistance R, R1 when itself connected between the, terminals 3 and 4,-and that sliding contact and contact 6 are preferably, mechanical-'- ly united or adjusted in unison with or by uni-control of those contacts and any other There is provided a control of'the input signal voltage, whereby, in case of unusually strong signals, the volume may be controlled by varying the screen grid or plate voltages of one or both of the tubes V and V1, and additionally by the signal input voltage control, the latter supplementing the former by a nice and fine control. The signal input control, in the exainple illustrated. is provided by shunting acrossthe input of one of the tubes. as V, a variab e portion of the resistance R2 of say 100,000 ohms connected to grid g of tube V and engaged by contact or slider 9 connected to cathode or ground. Again this contact or slider .9 is united mechanically for uni-control with'the slider or contact 6, and any other sliders or adjustable elements united with the latter in uni-control. The mechanical connection or uni-control is indicated by the broken line 10. By moving the contact 9 upwardly, the effective voltage impressed unon the input of the tube V is dellii creased, thereby decreasing volume of reproduction.

Where very strong signals are encountered, as from nearby broadcasting stations,

the screen grid and plate voltages and resistance R2 are simultaneously or in unison reduced. This reduces not only the efl'ective input signal. voltage but very greatly reduces also the amplification. While reduction of amplification by control of screen or control grid bias and plate voltage is in itself useful and effective, for very strong signals the con- ;trol of screen or control grid bias and plate voltage would have to be carried to such an extent suiiiciently to reduce the amplification, that the amplifying tube would be compelled to operate upon that portion of its characteristic related to screen or control grid bias that distortion, particularly of speech or music, would be introduced with a consequent loss of quality'of re roduction. By using in combination the a oresaid control of input signal voltage, of the type illustrated by way of example or of any equivalent type, the amplifica tion need not be so rigorously reduced, and. without loss of quality or introduction of distortion the volume may be further reduced by the signal input voltage control.

lVhile the control of input signal voltage is effected in the example illustrated at the input of an amplifier tube whose amplification is controlled, it will be understood that the input signal voltage control may be 10- catcd'at any other suitable position, preferably further in advance toward the antenna or absorption structure than indicated. In a superheterodyne system, it is preferred to control, as illustrated, the input voltage of the intermediate frequency. It will be understood, however, that such input signal voltage control may be applied to the input of the first detector tube D or at any suitable point in advance thereof.

While it may suflice to control the screen grid and plate voltages of one amplifier tube, either Vor V1. it is preferable to efi'ect the dual control of grid bias and plate voltage upon two or more of the amplifier tubes because. in event of strong incoming signals, if the volume control were confined to one or the first of the amplifier tubes only, to procure sufiicientlv low volume of reproduction. there would still exist very high amplification in the second or later amplifier tubes. giving rise to tube noises. To avoid these tube noises, it is preferred to apply the amplification con-' trol to two or more of the amplifier tubes.

While the signal input voltage control may also be duplicated at any suitable point in the system. it is preferredthat but'a single control of this type be utilized, and it is further preferred that it be applied to the firstof the amplifying tubes whose amplification is controlled. If, for example, a second input voltage control were applied to the second amplifying tube V1, there would result a reduction in the maximum amplifying power of the first tube or stage V. When located as shown. in the output system of the detector D Maximum 1 +160 +72 7 640,000 .2 85 +42 00, 000 3 45 +22 360,000 4 25 +12 5 7 50, 000 Minimum 5 10 5 880, 000

It will be noted that the internal plate impedance of the tube varies within relatively narrow range between 360,000 and 880,000 ohms.- The internal impedance varies from 640,000 ohms at maximum. amplification, through other magnitudemto 880,000 ohms at minimum amplification:

In the tuned loops L, .0, Fig. 4, for an intermediate or beat frequency of say 130 kilocycles, with an inductance L fourteen millihenries, the capacity C will be about 120 micromicrofarads, Each of these tunable loops by itself or disconnected has at resonance a resistance of about 800,000 ohms.

across its terminals. Accordingly by the volume control described the internal plate resistance remains for practical purposes substantially of the same order of magnitude or less than the. external plate impedance as viewed with respect to the tuned loop L, C.

In Fig. 5 the circuit arrangement is in general that of Fig. 4, like reference characters indicating corresponding parts in the two figures.

The input signal voltage control and plate.

voltage control are those of. the character descrlbed in connection with Fig.4. Their movable contacts 6 and 9 are mechanically coupled for operation in unison by the structure indicated at 10, which also operates the movable contact 11 slidable along the resistance R3 of say 150,000 ohms which, in the example illustrated, is in series between the terminals 3 and 'of the high tension source with the resistance P. The three sliders or contacts 6, 11 and 9 are moved in unison, and

in such senses that as the plate voltages upon the tubes 'V and V1, or either of them, are decreased, the negative bias upon the control grids g, or either of them, of the same tubes is increased. In the specific example illustrated, the slider contact 11 for this purpose will move upwardly while the slider 6 moves downwardly. Upward movement of slider 11 increases the positive potential of the cathode o with respect tocontrol grid 9 which 1,ses,ao'r

riation of volume or control of amplification with small or insubstantial efiect upon the magnitude of the internal plate resistance of the tube. i

In general, what has been said hereinbefore of the various circuits, including Fig. 4, applies as well to Fig. 5-.

. In Fig. 5 the screen gridvoltage is maintained substantially constant, and is obtained by tapping the end 8 of the conductor 7 to a suitable point on the resistance whose com- .ponents are R and R1, connected between the terminals 3 and 4, i. e., across the terminals of the high tension source, which is the arrangement described in connection with a variant of Fig. 4. In the present instance, however, the screen grid 'voltage is not variable the conductor 7 constitutes a fixed tap upon by the arrangement shown, and the end 8 of the resistance R, R1.

While generally not required, it may be understood, however, that the end 8 of the conductor 7 may be a slider uponthe resistance R, R1, which may be varied or moved either in unison with the contacts 6 and 11 and/or 9, either in a sense to give a cumulative effect with change in control grid bias, or an effect in opposition thereto.

My controls of the character hereinbefore described are not limited in their application to superheterodyne receivers. They are applicable equally to other types of receivers using screen grid tubes, for example, inradio frequency amplifiers. Figs. 4 and 5 serve to illustrate such receivers as well, since in any event the intermediate requency is a radio frequency. This is exemplified by omitting the first detector D, and relating to the input electrodes of the then first radio frequency amplifier tube .V a suitable coupling with an antenna or other absorption structure including or not, as desired, one or more cascaded tuned circuits. In such case, the condensers C may be of fixed magnitude tuning the radio frequency amplifier to a narrow band of frequencies, or, and generally, the condensers C will be variable for tuning to various frequencies within the broadcast or other range. It will be understood, however, both as to superheterodyne receivers and radio frequency amplifiers, that types of coupling not involving combinations of inductance and capacity such as L, G, may b employed.

What I claim is:

1. In the operation .of'a radio receiving system comprising an am lifier tube of the screen grid type, a moth of control which comprises carrying the plate voltage of the tube to effect a change in the-internal plate resistance thereof, and simultaneously so varying the screen grid voltage of the tube as to offset said variation of internal plate resistance and to effect a substantial change in the amplification by said tube.

system comprising an am lifier tube of the screen grid type, a metho of control which comprises varying the plate voltage of the tube to effect a change in the internal plate resistance thereof, and simultaneously so varying the negative bias upon the control grid as to offset said variation of internal plate resistance and to efi'ect a substantial change in the amplification by said tube.

3. In the operation of a radio receivingsystem comprising an amplifier tube of the screengrid type, a method of control which comprises varying the plate voltage of the tube to 'efiect a change in the internal plate resistance thereof, simultaneously so varying the bias of a grid of the tube as to olfset said variation of internal plate resistance and to decrease the amplification within the limit at which distortion occurs, and re- "is 2. In the operation of a radio receiving ducing the signal input voltage to. a degree effecting distortionless reproduction-of a ma nitude' less than that corresponding with said reduction of amplification.

4. In the operation of a radio receiving systemcomprising an am lifier tube of the screen grid type, a metho of control which comprises varying the plate voltage of the tube to effect a change in the internal plate resistance thereof, s multaneously so varyin the screen grid voltage of the tube as to 0 set said variation of internal plate resistance and to decrease the amplification within the limit at which distortion occurs, and reducing the signal input voltage to a degree effecting distortionless reproduction of a magnitude less than that corresponding with said reduction of amplification.

5. In the o eration of a radio receiving system comprising an am lifier tube of the screengrid type, a metho of control which plate voltage of the comprises varying the tube to effect a change in the internal plate resistance thereof, simultaneously so varying the negative-bias of a control grid as tooffset said variation of internal plate resistance and to decrease the amplification within the limit at which distortion occurs, and reducing the signal input voltage to a degree efl'ecting distortionless reproduction of a magnitude less than that corresponding with said reduction of amplification.

6. In the operation of a radio receivin system com using a tube of the screen gri type, ain t 0d of control which comprises lessthan that caused by said variation ofthe plate voltage, andmaintaining substantially constant theratio of the screen grid volta e to the late voltage.

7. he combination with an amplifier tube of the screen grid type, of means for varying the plate voltage, and means for simultaneously varying the bias voltage of a grid of said tube to vary the amplifying efiect of the tube while preventing abnormal change in the internal plate resistance thereof.

8. The combination with an amplifier tube of the screen grid type, of means for reducing the plate vpltage, and means for simultaneously reducing the screen grid voltage of said tube to reduce the amplifying eflect of the tube while preventing abnormal decrease in the internalplate resistance, thereof.

9. The combination with an amplifier tube of the screen grid type, of means for reducing the plate voltage, and means for simultaneously varying the negative bias of a control grid to reduce the amplifying eiiect of the tube while preventing abnormal decrease in the internal plate resistance thereof.

10. The combination with an amplifier tube of the screen grid type, of means for varying the plate voltage, means for simultaneously varying the screen grid voltage of said tube to vary the amplifying effect of the tube while preventing abnormal change in the internal plateresistance thereof, and means for maintaining substantially constant the ratio of the screen grid and plate voltages.

11. The combination with an amplifier tube of the screen grid type; of means for varying the plate voltage comprising a conductive impedance traversed by uni-directionalcurrent, means connecting with the plate of said tube 'for applying thereto voltages, corresponding with difi'erent points on said impedance, and-means for determining the ratio of the screen grid voltage to the plate volt age comprising a conductive impedance in shunt with the variable portion of said firstnamed impedance, and a connection from a.

point intermediate the terminals of said second-named impedance to the screen grid.

12. The combination with an amplifier tube of the screen grid type, of means for varying the plate voltage comprising a conductive impedance traversed by uni-directional current, means connecting with the plate of said tube for applying thereto voltages corresponding with different points on said impedance, and means for determining the ratio of the screen grid voltage to the plate voltage comprising a conductive impedance in shunt with the variable portion of said first-named impedance, and a connection from a fixed point intermediate the terminals of sdaid second-named impedance to the screen gm 13. In the operation of a radio receiving system comprising a. tube'of the screen grid type, a method of control which comprises simultaneously varying the plate voltage of the tube and the biasing voltage of a grid of the tube in such senses and to such relative extents that the internal plate impedance of the tube is varied to an extent difi'ering from that v type, a method of control which comprises decreasing the plate voltage-of-the tube, and simultaneously decreasing the biasing voltage of a grid of the tube while decreasing the difference between the plate and grid biasing voltages, thereby decreasing the internal plate impedance of the tube.

16. lln the operation of a radio receiving system comprising a tube of the screen grid type, a method of'control of amplification which comprises simultaneously varying the plate voltage of the tube and the biasing voltage of a grid of the tube cumulatively to effect a variation of the mutual conductance of the tube and didere-ntially to aflect the ratio of the internal to the external plate impedance of the tube. a

17. 1n the operation of a radio-receiving system comprising a tube of the screen grid type, a method of controlling the, amplification or volume of reproduction which coniprises simultaneously varying the voltages applied to the plate and a grid of the tube to vary the internal plate impedance of the tube through a range below the external plate circuit impedance.

18. In the operation of a radio receiving system comprisin a tube of the screen grid type, a method 0? controlling the amplification volume of reproduction which comprises simultaneously varying the. voltages applied to the plate and control gridof the tube to ,reduce the internal plate impedance of the tube below the external plate circuit inipedance.

19. In the operation of a radio receiving system comprising a-tube of the screen grid type, a method of controlling the amplification through a range, which comprises simultaneously varying the voltages applied to the plate and a grid of the tube, thereby varying the internal plate impedance of the tube to aaaaaov a magnitude higher, for a portion of a range, and to a magnitude lower, for another portion of said range, than the external plate circuit impedance.

20. .In the operation of a radio receivin system comprising a tube of the screen ri type, a methodof controlling the ampl cation through a range, which comprises simultaneously varying the voltages ap lied to the plate and screen grid of the tube, varying the internal plate impedance of the tube to a magnitude higher, for a portion of said range, and to amagnitude lower, for

another portion of said range, than the'external plate circuit impedance,

21. Radio receiving apparatus comprising a tube of the screen grid type,'means for varying the plate voltage of-said tube, and means for simultaneously 'varying the biasing voltage of a grid of said tube, in such senses and to such extents that the internal plate impedance of the tube is varied to an extent difiering from that caused bythe variationof plate voltage. a 11} I 22. Radio receiving apparatus .comprising a tube of the screen grid-"type, means for simultaneously varying the'plate voltage of the tube and the, biasing voltage of a grid of decrease of effect of the gri the internal plate impedance of the tube decreases.

the tubein such senses and tofsuch relative extents that for decrease ofilate voltage and biasing voltage,

.- 23. .Radio receiving apparatus comprising a tuhe'of the screen grid type, and means for controlling the volume of reproduction, adjustable for simultaneously decreasing the plate voltage and the biasing voltage of the grid of the tube to decrease the difierence between the plate and grid-biasing voltages thereby to decrease the internal plate impedance of the tube.

- 24. A radio receiving system comprising a tube of the screen grid t pe, means for simultaneously varyin the p ate voltage and biasing voltage applied to a grid of said tube, a second tube subsequent to said first tube and of the screen grid'type, and means for varyin the screen grid voltage of said second tu e simultaneously with the variation of plate and grid biasing voltages of said first tube by said first means.

' SARKES TARZIAN.

thereby CERTIFICATE OF CORRECTION. Patent No. 1,885,307. November l, 1932! SARKES TARZIAN.

it is hereby certified that error appears in the printed specification of the above numbered patent requiring correction'as' follows: Page 1, line 30, for "or" read "of": page 7, line 26, claim 22, before "means" insert the word "and";

' and same line, after "means" insert the words "for controlling the volume of reproduction, adjust-able"; and that the said Letters latent should be read with these' 'eorrections therein that the same may conform to the reeord'of the case in the Patent fiffiiee.

fi med err sealed thie are they of January A. l). W33. 

